Problem: $ { {4} \times \left[\begin{array}{r}{-1} \\ {0} \\ {-1}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{4}\times{-1} \\ {4}\times{0} \\ {4}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-4} \\ {0} \\ {-4}\end{array}\right]}$